/**
 * Computes the "brightness" of a color
 * Brightness is similiar to lightness in HSL but more closely approximates how humans perceive the
 * intensity of the different RGB components of a color. Brightness is sometimes called luminance.
 * Returns a number between 0% and 100%, where 100% is fully bright (white) and 0% is fully dark (black)
 * for color values.
 * For numbers and percentages it returns the same value to be used in @include filter(brightness(1.1)).
 *
 * Taken from Compass:
 * @link http://compass-style.org/reference/compass/utilities/color/brightness/
 */
@function brightness($color) {
  @if type-of($color) == color {
    @return (red($color) * 0.299 + green($color) * 0.587 + blue($color) * 0.114) / 255 * 100%;
  } @else {
    @return unquote("brightness(#{$color})");
  }
}
